1. Field of the Invention
The invention relates to fastener removal aid devices that permit efficient removal of fasteners, such as Hi-Lok® fasteners, including fasteners located in limited mobility or limited access locations.
2. State of the Art
Self-locking, permanently installed fasteners are commonly used in aerospace assembly to attach two parts. Hi-Lok® fasteners, sold by Hi-Shear Corporation, Torrance, Calif., are examples of such fasteners. As installed, Hi-Lok® fastener 100 is illustrated in FIG. 1 (Prior Art). The Hi-Lok® fastener 100 is a two-piece fastener consisting of a pin 102 having a threaded shaft 104, and a threaded collar 106. Hi-Lok® fasteners 100 are generally used for single use, high-strength, controlled, pre-load and permanent airframe assembly. Hi-Lok® fasteners 100 are made from metals and alloys such as titanium, aluminum and alloy steel and are the industry standard for high strength, permanently installed airframe fasteners.
The pin 102 of the fastener 100 is designed in two basic head styles—countersunk style and a compact protruding head style—and can accommodate both shear and tension applications. The threaded shaft 104 of the pin 102 has a hexagonal shaped recess 105 at its end opposite the head 103 to allow for one-sided installation.
The self-locking, threaded collar 106 generally includes a base portion 120 that transitions at 122 into a locking upset portion 124. The collar 106 has an internal counter-bore 114 at its base 120 to accommodate variations in material thickness. At the opposite end of the collar is a wrenching ring (not shown) that is torqued by a driving tool during installation until it shears off.
For installation, a passage 112 is drilled through the parts 108 and 110 to be fastened, which may be large sheets of metal, such as those found on aircrafts and boats. The threaded shaft 104 of the pin 102 is inserted through the aligned passages 112. The collar 106 is then hand rotated upon the threaded shaft 104 of the pin 102, the hexagonal shaped recess 105 in the pin 102 is then engaged to prevent relative rotation between the pin 102 and the structures 108, 110. Then, the collar 106 is controllably torqued with a wrench. The collar 106 is joined to a wrenching ring by a notched neck (not shown) on the collar 106 that shears from the threaded collar 106 at a predetermined torsional loading during torquing. The collar 106 provides a frictional spring lock to prevent the collar 106 from unthreading or loosening, even in environments of high vibration and stress. The torque at which the wrenching ring shears off (torque-off) determines the level of preload induced in the pin 102 and collar 106 assembly. Torque-off ranges can be selected for shear, tension and special applications.
Presently, removing self-locking, permanently installed fasteners, such as Hi-Lok® fasteners, can be cumbersome and laborious, because it can involve the removal of installed manufactured parts to access the fastener. To accomplish the removal of Hi-Lok® fasteners, manual, electric or air-motor drilling, utilizing a drill bit, are commonly employed to drill out the center of the shaft portion of the pin allowing the pin to be easily removed. Alternatively, cutting means, such as hack-saws or standard bolt cutters adapted for splitting collars, are used to cut the collars. If not done properly, the surrounding parts may become damaged, which can cause non-conformance (the reporting of which can be timely and costly). Poor fastener hole quality after removal can result, creating problems in refastening the parts using the same passages. Scars may also be left from the removal operation or consequential weakening may occur in the parts surrounding the passage, which may create premature structural fatigue failures in the surrounding structure or at the fastener holes.
Current problems with removing these self-locking, permanently installed fasteners are further compounded in areas where it is difficult to gain access to the fasteners, such as in locations where space is limited. Accordingly, the removal of self-locking fasteners without damage to the attached parts often presents a challenge.
Efforts have been made to address both the removal of the self-locking fasteners, and the speed at which these fasteners may be removed, without damage to the fastened parts. A rivet removal tool exists that is commonly available through aviation tool supply companies, such as BrownTool.com; however, this rivet removal tool is not intended for self-locking fasteners. Additionally, the rivet tool sits atop the fastener head and does not thread into a collar (i.e., a micro-stop type device) such as that used on certain self-locking fasteners. Accordingly, these types of removal tools are challenging to use in spaces, where it is difficult to maneuver.
Removing self-locking fasteners is necessary for repair and maintenance of the joined parts. For that reason, a need exists for a fastener removal aid device that facilitates the proper removal of frangible fasteners, such as Hi-Lok® fasteners. A need further exists for a removal aid that not only helps to minimize damage on the parts surrounding the fasteners, but also assists with the removal of fasteners in areas with very limited access and maneuverability.